Modulation



Oct. 3o, 1934. g, ROHNFELD. 1,978,693

MODULATION A Filed May 11, 1933 SVG/VAL .500365 SI/VAL .SOURCE INVENTOR JOHANNES Of//V/-ELD Y BY/fg ATTORNEY Patented Oct. 30, 1934 MODULATION Johannes Rohn-feld, Berlin, Germany, assignor to Telefunken Gesellschaft fur Drahtlose Telegraphie 1n. b. H., Berlin, Germany, a corporation of Germany Application May 11, 1933, Serial No. 670,389r In Germany May 11, 1932 4 Claims.

This invention relates to a transmitter arrangement comprising tubes connected in pushpull fashion at their inputs to a source of modunlating potentials and at their output electrodes 5to a tube or tubes in which high frequency oscillations are present and are to be modulated.

More in particular, this application is concerned with the combination of an audio frequency amplier and a radio frequency stage lovfmodulated by plate potential in which a modulator is employed as a push-pull amplifier which operates on the lower knee of the characteristic curve.

The coupling between the modulator stage 15fand the radio frequency stage is frequently effected by the aid of a transformer. However, this entails the drawback that the secondary winding of the transformer is traversed by the plate direct current of the radio frequency tube. 2-0`This results in a marked biasing saturation of the transformer so thatl an air-gap must be provided in order to minimize this effect. This, in turn, leads to the necessity of choosing larger transformer types inasmuch as the magnetic re- 2ulluctance of the transformer should not exceed a certain value. Now, the purpose of the present invention is to obviate the said shortcoming.

The nature of the present invention has been described in detail below with reference to the 39"1drawing in which:

Figure l shows a high frequency relay in which plate modulation is accomplished; While,

Figures 2 and 3 show modifications of the arrangement of Figure 1.

In Figure 1 the high frequency oscillations are impressed on the input electrodes of V1 from any source by way of a transformer, as shown, and are relayed and/or amplified in V1 and impressed from the output electrodes thereof on a load ciricuit, as shown. The oscillations, however, are modulated at signal frequency by a plate scheme. The signals are impressed from any source not shown on a pushpull amplifier 2, 4 and from thence to a transformer T, the secondary windfis'ing of which is connected, as shown, to the output of tube Vi.

According to one embodiment of the invention the combination of an iron-cored choke-coil 6 and a large condenser 8 is used for the purpose 5--0of shutting off the direct current from the secondary winding of the transformer, the condenser in this scheme being connected in series with the secondary Winding of the transformer,

, while the said choke coil is disposed in parallel to l" "the said series connection, as shown in Figure 2.

According to another embodiment of the invention, an auxiliary winding 10 is provided with and traversed by an auxiliary direct current, the ampere turns per second being so chosen that the magnetic field set up by the said auxiliary Winding will just counteract the field produced by the secondary winding traversed by the plate direct current; this auxiliary circuit in the said scheme containing an iron-cored choke coil; the inductance of which must be high enough in order that shor't-cirnuiting of the transformer may be avoided.

Having thus described my invention and the operation thereof, what I claim is:

1. The combination with a source of high fre- I quency oscillations' .and a source of signal potentials, of means for modulating said oscillations in accordance with said signal potentials comprising, a thermionic tube having input and out put electrodes, a circuit coupling said source of high frequency oscillations to said input electrodes, a thermionic tube having its input electrodes coupled to said source of signal potentials and its output electrodes connected to the primary Winding of a transformer, a circuit connecting the secondary winding of said transformer in series with the output electrodes of said rst named tube and with a source of direct current potential, and means connected with said last named circuit for preventing said secondary winding from becoming saturated due to the direct current component flowing therein.

2. In combination, a source of high frequency oscillations, a source of modulating potentials, a thermionic tube having input and output electrodes, a circuit coupling the input electrodes of said tube to said source of high frequency oscillations, a pair of thermionic tubes each having input and output electrodes, a circuit for connecting the input electrodes of said last named pair of tubes to said source of modulating potentials, a transformer, a circuit connecting the primary winding of said transformer to the output electrodes of said last named pair of tubes and to a source of direct current potential, a circuit connecting the secondary winding of said transformer in series with the output electrodes of said first named tube and with a source of direct current potential, and means connected with said last named circuit for preventing said secondary winding from becoming saturated due to the direct current component owing therein.

3. An arrangement as recited in claim 1 in which said means for preventing said secondary oli which said means for preventing said secondary from becoming saturated due to the direct current component flowing therein comprises a second winding on said transformer and a source of potential connected therewith for producing in said transformer an electrical field which opposes and compensates the field produced by the direct current component flowing in said secondary Winding.

JOHANNES ROHNFELD. 

